mjh Posted January 21, 2017 Share #21 Posted January 21, 2017 Advertisement (gone after registration) If you run Adobe's dng_validate on one of the as-shipped cameras' files you find something like this: LensSpecificationExif: 50.0 mm f/511.0 LensMakeExif: "Leica Camera AG" LensModelExif: "Apo-Summicron-M 1:2/50 ASPH." In my files, the maximum aperture value (MaxApertureValue) is specified correctly as 2.0. But this is part of the lens specs and has nothing to do with the guesstimated aperture which should correspond to the actually chosen f-stop, not the maximum aperture. Having said that there is a bug affecting the LensSpecification tag where the maximum aperture is wrong. But as the camera is well aware of the correct value (it is stored in the MaxApertureValue field after all), this bug must be unrelated to the guesstimated aperture issue. Link to post Share on other sites More sharing options...
Advertisement Posted January 21, 2017 Posted January 21, 2017 Hi mjh, Take a look here Leica M10 raw file (DNG) analysis. I'm sure you'll find what you were looking for!
scott kirkpatrick Posted January 21, 2017 Share #22 Posted January 21, 2017 Will covering the external light sensor mess up the in-camera lens corrections? It might. It forces the camera to think that the lens is wide-open. Sometimes the vignetting corrections are extra strong then, and are phased out as the lens is stopped down. Getting this wrong may give you artificially lightened corners or edges with an inappropriate color correction. scott Link to post Share on other sites More sharing options...
pico Posted January 21, 2017 Share #23 Posted January 21, 2017 [...] I do understand why they're fed up with users complaining it's inaccurate! Perhaps we could set the nay-sayers right by demonstrating that regardless of their complaints, the camera operates properly to make their exposures good. Should the nays persist in complaints that they want control of the EXIF, then give them what they want along with a retraction of their warranty. (Is there a field in the DNG standard for 'asshole user'?) Link to post Share on other sites More sharing options...
scott kirkpatrick Posted January 21, 2017 Share #24 Posted January 21, 2017 @mjh -- Without having the (long) Adobe DNG specs handy, I can't tell you for sure whether "LensSpecificationExif" is a static specification, and the error message means that two specifications which should be duplicates do not agree, or that it is really the place where lens focal length (which changes in zoom lenses) and aperture are supposed to be recorded. I passed this one earlier today to Sandy McGuffog to check into. Are you also running dng_validate, or one of the ExifReaders that are available? scott Link to post Share on other sites More sharing options...
scott kirkpatrick Posted January 21, 2017 Share #25 Posted January 21, 2017 Nay-sayers have a powerful and not very constructive influence. The whole discussion of how nothing but pure optical corrections is appropriate to give a fine Leica lens its character is another area in which otherwise reasonable people turn into trolls and feast. Let's not go there (yet). scott Link to post Share on other sites More sharing options...
pico Posted January 21, 2017 Share #26 Posted January 21, 2017 Nay-sayers have a powerful and not very constructive influence. The whole discussion of how nothing but pure optical corrections is appropriate to give a fine Leica lens its character is another area in which otherwise reasonable people turn into trolls and feast. Let's not go there (yet). scott Thank you for your cogent advice and taking the angst from my post. I am in a bad mood. Link to post Share on other sites More sharing options...
waterlenz Posted January 21, 2017 Share #27 Posted January 21, 2017 Advertisement (gone after registration) In my files, the maximum aperture value (MaxApertureValue) is specified correctly as 2.0. But this is part of the lens specs and has nothing to do with the guesstimated aperture which should correspond to the actually chosen f-stop, not the maximum aperture. Having said that there is a bug affecting the LensSpecification tag where the maximum aperture is wrong. But as the camera is well aware of the correct value (it is stored in the MaxApertureValue field after all), this bug must be unrelated to the guesstimated aperture issue. The max aperture comes from the lens model that is in the code on the lens mount- with my M8 different differ versions (I have been using LR since version 1) of Lightroom get the lens model right if at all. I have seen differences as well with Canon lenses so when using metadata to find pix taken with a certain lens one has to look at two different names for the same lens model. I seem to be stuck with the metadata based on the version of LR from when I originally uploaded the image. Link to post Share on other sites More sharing options...
pico Posted January 21, 2017 Share #28 Posted January 21, 2017 The max aperture comes from the lens model, which intrinsic to the code on the lens mount. However, actual aperture is not transmitted to the camera from the lens in M cameras (unlike most other digital cameras) so has to be estimated from light measurements done by the camera hence the external light sensor plus light coming through the lens. So should not the external light sensor be eliminated? In my modest, naive experience it has never been useful. Get rid of it and we move back to the principle basics. M11 - no light sensor. . Link to post Share on other sites More sharing options...
waterlenz Posted January 21, 2017 Share #29 Posted January 21, 2017 So should not the external light sensor be eliminated? In my modest, naive experience it has never been useful. Get rid of it and we move back to the principle basics. M11 - no light sensor. . This could be extremely problematic for fixing light falloff issues related to the short back focus distance of Leica M lenses. Link to post Share on other sites More sharing options...
pico Posted January 21, 2017 Share #30 Posted January 21, 2017 This could be extremely problematic for fixing light falloff issues related to the short back focus distance of Leica M lenses. Explain please. . Link to post Share on other sites More sharing options...
scott kirkpatrick Posted January 21, 2017 Share #31 Posted January 21, 2017 So should not the external light sensor be eliminated? In my modest, naive experience it has never been useful. Get rid of it and we move back to the principle basics. M11 - no light sensor. . No, the external sensor is the only evidence we have to drive certain internal correction routines that depend upon aperture. It was never really meant for our entertainment. But if you are out testing things, and don't keep careful notes, it can be very helpful in sorting out the sequence of steps taken, so I will miss it if it is gone. scott Link to post Share on other sites More sharing options...
waterlenz Posted January 21, 2017 Share #32 Posted January 21, 2017 Explain please. . See Scott's post. BTW many if not most digital cameras do some internal lens correction, however, they rely on the electronic transmission of data from the lens via the contacts that you see on or near the lens mount on most lenses these days. Lenses have various chips in them as well. So the camera "knows" which model lens is attached as well as aperture, focus distance, and focal length (zoom lenses). An M only "knows" the basics from the lens model. Link to post Share on other sites More sharing options...
pico Posted January 21, 2017 Share #33 Posted January 21, 2017 No, the external sensor is the only evidence we have to drive certain internal correction routines that depend upon aperture. It was never really meant for our entertainment. There is no EXIF information that indicates what the little sensors sees. No? Okay, if that suits you. I use no lens identification whatsoever and am perfectly happy. I'll tape over the sensor and suggest that Leica eliminates it. Really, I cannot imagine how it is useful. Call me a skeptic. It might be interesting when someone brighter than I could show us what the tiny window sees. . Link to post Share on other sites More sharing options...
uhoh7 Posted January 21, 2017 Share #34 Posted January 21, 2017 Great service, thank you, Sandy. You note the color matrix in the RAW file suggests sensor is different. Would not the same sort of differences be seen with a different choice of IR cut in the coverglass, since the IR cutoff curves vary greatly between say a schott S8612 and BG55 in the visible spectrum? IE the sensor is the same but IR cut has been changed. It would be interesting on this same note to compare M9 files before and after the current sensor upgrade which involves such a change. Could you elaborate a bit on the color matrix, and it's relation to sensor design, or suggest a link? Thanks so much Link to post Share on other sites More sharing options...
mjh Posted January 22, 2017 Share #35 Posted January 22, 2017 I can't tell you for sure whether "LensSpecificationExif" is a static specification, and the error message means that two specifications which should be duplicates do not agree, or that it is really the place where lens focal length (which changes in zoom lenses) and aperture are supposed to be recorded. There are (I think) three Exif tags referring to the maximum aperture. First there is the MaximumApertureValue tag with a rational value; this one appears to be correct. Then there is the LensModel tag with a string value; this appears to be correct as well. And then there is the LensSpecification tag with up to four rational values for the shortest focal length, the longest focal length, the maximum aperture for the shortest focal length, and the maximum aperture for the longest focal length. For a prime lens, only two values would be specified, the focal length and the maximum aperture. This is the value that the M10 gets wrong, for whatever reason. I guess it is something trivial. Are you also running dng_validate, or one of the ExifReaders that are available? Just ExifTool. Link to post Share on other sites More sharing options...
ramarren Posted January 22, 2017 Share #36 Posted January 22, 2017 You are correct, it was deliberately omitted on the M10. But I don't understand why. It wasn't perfect data, but it was still useful...far better than nothing. I don't really care much one way or the other, but I look to EXIF data to tell me specific and correct information when analyzing problems. Incorrect or approximate information is actually worse than no data at all, IMO. I'm not sure that the cameras use the aperture information in the exposure to influence the application of the lens profile. Does anyone know for sure? Link to post Share on other sites More sharing options...
digitalfx Posted January 22, 2017 Share #37 Posted January 22, 2017 I don't really care much one way or the other, but I look to EXIF data to tell me specific and correct information when analyzing problems. Incorrect or approximate information is actually worse than no data at all, IMO. I'm not sure that the cameras use the aperture information in the exposure to influence the application of the lens profile. Does anyone know for sure? then ignore the info. Link to post Share on other sites More sharing options...
waterlenz Posted January 22, 2017 Share #38 Posted January 22, 2017 There is no EXIF information that indicates what the little sensors sees. No? Okay, if that suits you. I use no lens identification whatsoever and am perfectly happy. I'll tape over the sensor and suggest that Leica eliminates it. Really, I cannot imagine how it is useful. Call me a skeptic. It might be interesting when someone brighter than I could show us what the tiny window sees. . If you do this it may be like using an M lens on a Sony apha7 series camera (in other words you will regret it) - there are lots of posts on this forum about this. Link to post Share on other sites More sharing options...
digitalfx Posted January 22, 2017 Share #39 Posted January 22, 2017 the sensor is used to adjust the brightness off the framelines Link to post Share on other sites More sharing options...
scott kirkpatrick Posted January 22, 2017 Share #40 Posted January 22, 2017 I'm not sure that the cameras use the aperture information in the exposure to influence the application of the lens profile. Does anyone know for sure? I tested for this a while back, and wqs able to see a difference in the vignetting corrections between wide open lens and, say, f/5.6, shooting a white wall to exhibit the colors at the edge of a frame. And Sean Reid, who is even more compulsive about this stuff, says there definitely is. scott Link to post Share on other sites More sharing options...
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